1176 FAT METABOLISM [pt. iii 



acid content up to hatching. Bialascewicz & Mincovna used two 

 methods, that of Kumagawa-Suto and that of Bang, obtaining sub- 

 stantially the same results with each, while Faure-Fremiet & Dragoiu 

 used that of Kumagawa-Suto alone. Still later Barthelemy & Bonnet 

 fully confirmed the loss of fatty acids over the whole of development 

 found by Bialascewicz & Mincovna, noting a loss of 0-102 mgm. per 

 embryo, instead of o- 192. They did not, however, make any estimations 

 on the just-hatched embryos, and so had nothing to say on the 

 difference between Faure-Fremiet & Dragoiu and the other workers. 

 Possibly the breed of frog used may account for this. In any case we 

 shall assume here that practically no fat disappears from the am- 

 phibian egg before hatching, but that afterwards a considerable 

 utilisation takes place. The rate at which the fatty acids disappear 

 was sketched out by Bialascewicz & Mincovna in a few experiments, 

 and is shown in Fig. 368, where in the upper graph the amount of 

 fatty acids disappearing from one larva per day is plotted against 

 the time. The curve rises more or less steadily. For the sake of 

 comparison the curve of protein utilisation established by Bialasce- 

 wicz & Mincovna is placed beside it, and we thus see how at a 

 certain point the combustion of protein attains a maximum and 

 afterwards falls away, giving place to the catabolism of fatty acids. 

 Below is placed a composite graph showing the utilisation of protein 

 and fat by the chick embryo (taken from Figs. 325 and 360). The 

 likeness between the two pictures is quite striking. Not only do both 

 embryos exhibit a peak of protein catabolism, but the peak comes at 

 approximately the same epoch of development, and this although 

 the frog derives 70 per cent, of its waste energy from protein and 

 the chick only 5 per cent., and although the time of hatching in the 

 two organisms is so completely different. For various reasons, which 

 have already been stated, we cannot add curves for carbohydrate 

 catabolism to the pictures, nor have any other embryos been investi- 

 gated in sufficient detail to permit of parallel graphs being drawn for 

 them. In the case of mammahan and selachian embryos, indeed, it is 

 possible that we have already the descending limb of the peaked pro- 

 tein cataboHsm curve (see p. 1 1 17), and Hayes' account of the consti- 

 tution of the embryo of the Atlantic salmon {Salmo salar) , which shows 

 a rising fat-content up to the io6th day from fertilisation, followed 

 by a fall, may indicate a late onset of fat catabolism in that case also. 

 But to return to the fat metabolism of the frog embryo, the relations 



